The hydrogenation of 2-butyne-1,4-diol in propan-2-ol over a carbon-supported palladium catalyst has been investigated in a batch reactor. At low conversions complete selectivity to cis-but-2-ene-1,4-diol is observed. However, further hydrogenation leads to a wide variety of products, most notably 2-isopropoxy-tetrahydrofuran and butane, neither of which have previously been associated with this reaction system. The former is thought to occur as a result of a surface-mediated process, involving the insertion of dissociatively adsorbed solvent molecules. Butane formation is attributed to the double condensation and hydrogenation of a chemisorbed cis-but-2-ene-1,4-diol intermediate. The alkane preferentially partitions in the gaseous phase, which results in an marked mass imbalance for the liquid phase. A reaction scheme is presented to rationalise these observations.

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The hydrogenation of a mixture of cis-and trans-1,3-pentadiene over a 1% Pd/Al 2 O 3 catalyst at 303 K has been studied using infrared spectroscopy to monitor the changes in the composition of the gas phase over the catalyst as a function of time. The reaction is seen to occur as a consecutive process, with the terminal double bond hydrogenated in advance of the internal double bond. Vibrational assignments have been confirmed through ancillary calculations for a number of C 5 molecules. The reaction profile is consistent with the catalyst presenting two distinct reaction sites: hydrogenation of the terminal double bond occurs at Site a, whilst Site b is responsible for hydrogenation of the internal double bond. Trans-pent-2-ene is identified as the only reaction intermediate. From comparative studies of the hydrogenation of pentenes over the catalyst, the absence of any cis-pent-2-ene in the reaction mixture is tentatively attributed to cis-1,3-pentadiene isomerising at Site a to form trans-1,3pentadiene. The effect of toluene-d 8 to act as a chemical modifier was also investigated and shown to selectively poison Site b, Site a being unperturbed.

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